Porous Silicon Fabrication for MEMS Applications

We describe the use of porous silicon fabrication technique for fabricating non-manhattan structures in silicon using wet etching. The fabrication method is simple to set up, economical and produces smooth etched surface. A solid source diffusion of N++ in a P type wafer with low stress thermally grown silicon nitride is used as a masking layer. Comparison of porous silicon etches with wafers solid source diffusion and implanted diffusion is presented. The result show that areas where a solid source diffusion is used form an etch angle of 70-80, however using an implanted diffusion the etch angle is closer to 90. The selectivity of the etch during porous silicon fabrication using any of the above two as masking layer results in fabrication of high aspect ratio non-manhattan structures. These structures since are wet etched do not have surface roughness and can be used for optical applications.